I know, but it is accented ἔστι when it means "there is." I don't think the sentence above was meant to mean "perhaps a disease in this wing is bad," but rather, "perhaps there is a bad disease in this wing."

But I don't understand, Sidgwick says that the adjective must always go with the article when is attributing something to a noun, because if not, it's meaning becomes predicative instead of attributive. Here it is (bold is mine):

I. The Article ὁ, ἡ, τό gives a good deal of trouble to the learner before its use is fully mastered, and it is best therefore to explain the main points about it at the very first.There is not word in Greek for a, an: it is simply ommited: or the Indefinite Pronoun τις, 'a certain one', is used. The Greek Article means the, and it is used (broadly speaking) whereever we use the, but also in some places where we do not. It is these latter which constitute the difficulty to the beginner.

2. Position of the Article with Adjectives.

In english we say 'the bad man'; and if we wish to translate into Greek, the point to observe is that the adjective must have the article.The order of Adjectives and Substantives may be inverted if we please. Thus we may say either ὁ κακός ἀνήρ, or ὁ ἀνήρ ὁ κακός; but in either case the Adjective must have the Article.If this rule is broken, as it is often by beginners, and if we write ὁ ἀνήρ κακός, or κακός ὁ ἀνήρ, the phrase is still good Greek, but the meaning is quite altered; it is no longer 'the bad man', but 'the man is bad'. The adjective, by being deprived of the article, has ceased to be an attribute, and has become a predicate.

So I don't understand why the answer key is not putting the article to the adjectives πολλοὺς and κακή:

huilen wrote:But I don't understand, Sidgwick says that the adjective must always go with the article when is attributing something to a noun, because if not, it's meaning becomes predicative instead of attributive...So I don't understand why the answer key is not putting the article to the adjectives πολλοὺς and κακή:

ὁρῶ [τοὺς] πολλοὺς κύκνους, οἱ λαμπροὶ ἐισι καὶ λευκοί.

ἴσως [ἡ] κακή ἐστι νόσος ἐν τούτῳ τῷ πτερῷ.

What Sidwick is saying is that IF the article is to be used, it has to go right before the adjective for the phrase to be attributive not predicate. But in these examples the nouns are presumably indefinite, so you don't need any articles.

Probert, A New Short Guide to the Accentuation of Ancient Greek (Bristol Classical Press 2003) discusses the paroxytone accentuation of ἔστι (sec. 282, pp. 144-6).

To summarize, the argument that ἔστι was paroxytone when it expressed existence or possibility and could not be omitted (as well as when it was the first word in a sentence or verse, or followed certain function words) was formulated by Hermann (1801), based on a statement attributed to Herodian (2d century CE), as well as some obscure remarks by the Byzantine scholars Photius (9th c.) and Eustathius (12th c.). (Most of what we know of Herodian's work on Greek accentuation is derived from the scholia found in the 9th or 10th century ms. of Homer, the Codex Venetus, or "A".)

Wackernagel (1877) challenged Hermann's view, asserting that the paroxytone accentuation was only determined by position, not by meaning, based on historical linguistics. W.S. Barrett's edition of Euripides' Hippolytus discusses the point (App. II, pp. 425-6), coming down in favor of Wackernagel. M.L. West, in the preface to his Teubner edition of Aeschylus, also adopts Wackernagel's position (p. xxxi).

Barrett outlines Wackernagel's argument, which I haven't been able to obtain access to. Basically, comparative Indo-European linguistics show that finite verbs were originally enclitic, except when in sentence-initial position. Eventually finite verb-forms acquired recessive accent in Greek, except for most of the present-tense forms of εἰμι and φημι, but, in Wackernagel's view, these continued to be accented in word-initial positions and after οὐ, based on position, not meaning. (There is also a dispute as to whether ἔστι is paroxytone after function words other than οὐ.) That's a very inadequate summary of the argument, but I'm sure that Wackernagel's discussion, which I haven't seen, would have much fuller and more compelling than I'm able to frame it.